In no particular order (off the top of my head)
Guilty Gear
-Top notch heavy metal instrumentals. Every song sounds iconic, unique, and excellent.
Blazblue
-IMO the original games (Calamity Trigger) soundtrack was kind of hit and miss, and most of the remixes in Chrono Phantasma made it even worse, but overall there are a shit ton of amazing themes throughout the series that are on par with Guilty Gear. The "X character vs Y character" themes are pretty consistently amazing imo.
Marvel Super Heroes
-Like all the Marvel games, I don't think this one rises to the level of something like Guilty Gear, but there are some amazing tracks scattered throughout the franchise, and MSH has the highest concentration of them IMO.
Under Night In-Birth
-Same sound as Metly Blood mostly, but a step above it in terms of consistent quality
Melty Blood
-Really varied and pretty memorable tracks.
Skullgirls
-Well, yeah.
Third Striker
-Stylish, unique, and very memorable.
Maybe not the best, but MvC2's soundtrack is criminally underated. Always pains me when I watch old matches when I watch old match videos and the soundtrack is hacked to some run of the mill electronic shit.
I must admit, some of the tracks in mvc2 are pretty nice. Ultimately though, I tend to use custom soundtracks for even games I like when I've played them for hundreds of hours straight (only exceptions being when it's truly one of my most beloved soundtracks ever, like Guilty Gear, SMT, or
Ketsui). And Mvc2's kinda good but somewhat unfitting for fighting music tends to end up getting swapped out for other tracks when I'm playing it on ps3 and voice chat isn't turned off.